1. Field of the Invention
The invention relates to signal sensing and, more particularly, to a method for sensing input signal changes at an input of an input/output module operated in an automation system, where a signal is sampled by the input/output module, a change event and a timestamp associated with the change event is generated when a change in the sampled signal occurs, and a value pair comprising the change event and the timestamp is stored in an automation component having a higher-ranking than the input/output module.
2. Description of the Related Art
In automation systems, i.e., in decentralized stations using fieldbus/PROFIBUS-DP or PROFINET, input/output modules are connected preferably by an interface module. It is through input/output modules that signal changes from digital or analog peripherals are sensed, analyzed and provided with a time of day. The time of day is configured as a timestamp. Making use of the timestamping of signal changes is particularly important to be able to analyze a chronological sequence of events (SOE) at a later stage. An example of such an input signal change is a change in a binary input signal, or a state change or the like. Within the meaning of the present invention, an input signal change is also to be understood as meaning that a limit value of an analog signal has been exceeded.
DE 10 2006 010 748 A1 discloses a method for recording input signal changes. On the other hand, it is known in automation devices having decentralized peripherals that are connected to the interface module to implement a function that analyzes a signal change from, for example, a digital peripheral and provides said signal change with a timestamp accordingly. This means, however, that the time instant recorded in the timestamp is the time of day of the clock in the interface module at the moment of the transfer of the user data from the peripheral module, preferably the input/output module, and as a consequence is different from the time instant of the actual recording of the signal on the peripheral module or, as the case may be, the input/output module. With the method described in DE 10 2006 010 748 A1, it is disadvantageous that in order to record the input signal change on the input/output modules each input/output module requires an implementation or hardware for a high-precision clock. On the other hand, it is a disadvantage of the known methods having the decentralized peripherals that the timestamp is not determined with a sufficient degree of precision.